BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDRA. 115 



Concerning the process in Geophilus, P. et M. Bonin state in a brief 

 paper (:03) th.it the axial filament is not formed from the substance of 

 the distal centrosome, as " ce dernier se distingue toujours avec son con- 

 gt-nere, au niveau de son extremite." The results of Collin (:Ol) upon 

 the same material are similar in this respect. 



From these results and my own on Scolopendra heros, I believe it 

 is safe to conclude that the axial filament is not formed from centro- 

 some substance, but arises in the vicinity of the centrosome as a differ- 

 entiation of the archoplasmic portion of the cytoplasm. It has been 

 noted that, during the early stages of metamorphosis, when the axial 

 filament is still enclosed in the mass of archoplasm, it is immediately 

 surrounded by a mantle of this substance, which shows its differentiation 

 from the rest of the archoplasm by its less granular and more transparent 

 appearance. I have observed in Lithobius about the same condition in 

 much more advanced cells, in which the axial filament has attained a 

 considerable length ; but in Lithobius it is apparently the cytoplasm 

 which shows this differentiation. This, however, I do not consider as 

 a fundamental difference, for, as we have setn, the archoplasm in the 

 resting cells of Scolopendra is but slightly differentiated from the ordinary 

 cytoplasm. Further evidence, though indirect, of the cytoplasmic 

 origin of the axial filament is furnished by those peculiar formations 

 arising in the cytoplasm of the lengthening spermatid which I have 

 described under the name of pseudo-axial filaments. These are similar 

 in structure and staining reaction to the true axial filament in its early 

 stages; but there can be no doubt that these are formed from the cyto- 

 plasm or the disseminated archoplasm. They are entirely distinct in 

 their origin from the centrosomes, which certainly contribute nothing 

 to their formation. 



The migration of portions of archoplasm along the axial filament I 

 consider as additional evidence pointing toward the archoplasmic origin 

 of the filament. In insects the Nebenkern has often been figured as 

 breaking up into smaller portions which migrate along the filament. In 

 material in which this has been described, however, the cells were usually 

 so small that the fate of these structures could not be followed as clearly 

 as is possible in the large spermatids of Scolopendra. Here the migra- 

 tion of the archoplasm occurs just at the time when the cell and axial 

 filament are lengthening very rapidly, therefore at a time when this 

 material can be used in building up this filament. As the axial filament 

 continues to lengthen, these masses become smaller and fainter, and 

 finally disappear entirely. 



